Microwave switch



Sept. 7, 1965 A. E. COHEN MICROWAVE SWI TCH Filed May 21, 1963 5Sheets-Sheet l SWITCH ACTNLIJAZION FIRST 22 NS I MICROWAVE ENERGY souRcESAMPLED OUTPUT sIGNAI.

SECOND MICROWAVE ENERGY SOURCE FIG. I

SAMPLED FIRST MICROWAVE MICROWAVE OUTPUT ENERGY souRcE CYCLICALTWO-STATE BACK-BIAS souRcE SECOND MICROWAVE ENERGY souRcE .4

FIG. 2

INVENTOR. ARTHUR E. COHEN ATTORNEY Sept. 7, 1965 A. E. COHEN MICROWAVESWITCH 3 Sheets-Sheet 2 Filed May 21, 1963 FIG. 3

INVENTOR.

ARTHUR E. COHEN ATTORNEY p 7, 5 A. E. COHEN 3,205,493

MICROWAVE SWITCH Filed May 21, 1963 3 Sheets-Sheet 3 R 42/-\ VARACTOR 2LIMITER SOURCE SW'TCH souRcs VARACTOR LIMITER FIG. 5

saw

l9 SOURCE MICROWAVE ENERGY SQURCE 38 FIG. 6

INVENTOR.

ARTHUR E. COHEN ATTORNEY United States Patent 3,205,493 MICROWAVE SWITCHArthur E. Cohen, Anaheim, Calif., assignor to North American Aviation,Inc. Filed May 21, 1963, Ser. No. 281,973 .10 Claims. (Cl. 3435) Theconcept of this invention relates to mean-s for switching microwaveenergy, and more particularly to improved microwave switch meansoperable at very high frequencies.

With the increased application of microwave data processing systems,means have been sought for high-speed switching of microwave energy atspeeds, for example, above 1 megacycle per second. In this Way,microwave data processing equipment such as microwave signal devices maybe time-shared between several microwave signal sources or channels, soas to reduce the total amount of signal devices or amplifiers requiredin a given system or equipment.

Such high-speed switching of microwave energy may be accomplished bymeans of a device whose capacitive reactance can be varied by anelectrical signal such as a varactor diode shunted across the narrowdimension of a waveguide section, and then by applying a suitable biasvoltage across the diode. The varactor, 0r p-n junction semiconductor,when operated as a back-biased junction diode, behaves as a variablecapacitance the value of which varies as a function of the applied bias.Hence, by shunting such a device across a waveguide section andadjusting the bias across the diode, an adjustably tuned or conductivemicrowave switching device can be achieved. By means of the adjustmentof the bias across the diode, the microwave combination of waveguidesection and back-biased junction diode (or varactor) may be tuned so asto transmit microwave energy of a preselected frequency thru thewaveguide section in either direction. Also, the bias (and associatedcapacitance) may be varied as to dc-tune the microwave combinationwhereby a reflection of microwave energy is obtained, rather thantransmission thereof. Further, the response time of such varactor (to achange in the state of the applied backbias) is extremely low, responsetimes as low as second being obtainable. Moreover, such devices aresubstantially no-loss devices, producing very little attenuation of themicrowave energy applied to the waveguide. Hence, it is to beappreciated that high speed microwave switching may be obtained. Bycombining the microwave switch in novel combination with a plurality ofwaveguides and multi-port non-reciprocal microwave signal attenuatingdevices such as ferrite circulators, highly useful multi-functionswitching may be achieved.

A concept of the invention is to provide efiicient solidstate microwaveswitch means, adapted to function as a high-speed switch for microwavesignals such as radar transmitter signals and radar receiver signals.

In a preferred embodiment of the invention there is provided a first andsecond microwave circulator having at least three ports, a respectivefirst port of which is connected to a first and second sourcerespectively of microwave energy. A microwave switch employing avaractor diode shunted across a waveguide section, interconnects thesecond ports of the two circulators. The third port of one of thecirculators serves as an output port, while the third port of the othercirculator may be shorted thru a dummy load impedance.

In normal operation of the above described arrangement, a bias isapplied across the varactor to operate the microwave switch wherebyalternately the first microwave energy source is connected to thecirculator output port while the second source is shorted through theload impedance, then the second microwave energy source is connected tothe circulator output port while the first source is shorted through theload impedance. In this way, the combination of two circulators andmicrowave switch cooperate as a time-sharing switch, to provide samplingof the two sources of microwave energy.

Accordingly, it is an object of the subject invention to providehigh-speed switching of microwave signals.

It is another object ofthe subject invention to provide means forhigh-speed sampling of several sources of microwave energy.

It is still another object of the invention to provide microwavesampling means requiring only one varactor for sampling a plurality ofreceived microwave signals.

Yet another object of the invention is to provide an effective microwaveswitch for use in a time-shared monopulse receiver.

A further object of the subject invention is to provide an efficientmulti-function microwave switch useful in a monopulse radar system.

These and other objects of the invention will become apparent from thefollowing description taken in connection with the accompanying drawingsin which:

FIG. 1 is a functional block diagram illustrating a concept of theinvention.

FIG. 2 is a functional block diagram of one embodiment of the invention.

FIG. 3 is an isometric view showing the construction and arrangement ofthe microwave switch of FIG. 2.

FIG. 4 is a partial vertical section of the device of FIG. 3.

FIG. 5 is a functional block diagram of an alternative embodiment of theinvention.

FIG. 6 is a functional block diagram of another embodiment of theinvention.

In the drawings, like reference characters refer to like parts.

Referring to FIG. 1, there is illustrated a simplified schematic diagramof a concept of the invention. There is provided a double-poledouble-throw switch 21 for switching microwave signals, and having afirst and second armature 22 and 23. First and second armatures 22 and23 are connected to a first and second microwave energy source-s 12 and13, respectively. Also provided are first and second switching terminals24 and 25 associated with first armature 22, and first and secondswitching terminals 26 and 27 associated with second armature 23. Afirst switching terminal associated with each of the two armatures isinterconnected with a second terminal associated with the other of thetwo armatures. In other words, terminals 24 and 27 are interconnected,and terminals 25 and 26 are interconnected. Terminal 27 is also shortedto ground by means of a shorting impedance 16, and terminal 25 serves asan output terminal connected to an output line 15. As illustrated inFIG. 1, the pair of armatures 22 and 23 are shown positionedintermediate the two switching positions employed.

There is further provided switch actuation means 19 in cooperation withswitch 21 for alternately switching the armatures from engagement withone to the other of the associated first and second switching terminals.

In normal operation of the above described arrangement, first onemicrowave signal source is connected to output line 15, while the othermicrowave signal source is shorted thru shorting impedance 16; and thenthe other microwave signal source is connected to source terminal 15,while the first source is shorted thru impedance 16. In this way, outputline 15 is made to sample alternately the two microwave energy signalsources 12 and 13 in FIG. 1.

It is to be appreciated that the switch 21 of FIG. 1 is only afunctional schematic representation of means for sampling a plurality ofsignal sources. Switching means more suitable for cooperation with aplurality of microwave energy sources is shown in FIG. 2.

Referring to FIG. 2, there is illustrated a functional block diagram ofone embodiment of the invention. There is provided a first and secondmicrowave circulator and 11 having at least three ports. A respectivefirst port of circulators 1t) and 11 is connected to a first and secondsource 12 and 13, respectively, of microwave energy. A microwave switch14 interconnects the second ports of first and second circulators 10 and11. A third port of first circulator 10 provides an output to line 15,and the third port of second circulator 11 is shorted by a dummy loadimpedance 16. Such load impedance is a matched termination which maycomprise a waveguide section, having a piece of tapered microwaveabsorptive or lossy dielectric inserted therein parallel to thelongitudinal axis thereof, whereby microwave attenuation withoutreflection is achieved, as is well understood in the art.

Microwave circulators 10 and 11 are multiport nonreciprocal orunidirectional microwave attenuators which demonstrate a low impedancebetween adjacent ports to signals transported in the direction indicatedby the curved or circularly shaped arrows in FIG. 1. The circulatorsdemonstrate a relatively high impedance between adjacent ports to signaltransport in a direction opposite that indicated by the curved arrows.Also, a large impedance is exhibited between non-adjacent ports. Hence,in first circulator 10 of FIG. 1, for example, signals may fiow frommicrowave source 12 to the first port of circulator 1t) and then out thesecond port of circulator 10 to switch 14 without significantattenuation. However, such applied signals will not be transmitted frommicrowave source 12 to output port 15 without substantial attenuation.Similarly, an input applied to the second port of circulator 10 willappear substantially unattenuated at the third port of circulator 10(e.g., at output line 15).

Microwave circulators 10 and 11 are similarly constructed and arranged,preferably being of the ferrite type and similar, for example, to ModelCX-405 manufactured by Rantcc, Inc., of Calabasas, California.

Microwave switch 14 is comprised of a microwave section 17 adapted toprovide microwave communication between circulators 1t and 11, and avaractor diode 18 shunted across waveguide section 17 and connected to asource 19 of switching signals. The switching signals provided by source19 are two-state signals one of which adjusts the back-bias upon, andhence the capacitive effect of, diode 18 within waveguide section 17 soas to allow microwave communication between the ends of waveguidesection 17. The second state of the switching signal is selected toadjust the capacitive effect of diode 18 within waveguide section 17whereby the combination 14 substantially reflects, rather than conducts,microwave signals applied at either end of waveguide section 17.

The construction and arrangement of microwave switch 14 is shown indetail in FIGS. 3 and 4.

Referring to FIGS. 3 and 4, there is illustrated, respectively, anisometric view and vertical center section (the vertical center sectionbeing taken along the longitudinal waveguide axis shown in theisonmetric view) of a preferred embodiment of microwave switch 14. Thereis provided a rectangular waveguide section 17 of preferably reducedheight, the height being adequate to accommodate no more than thelongitudinal dimension of the ceramic or reactive element of a varactordiode 18, which is placed across the narrow dimension of waveguidesection 17 so as to present a microwave shunt impedance. It ispreferable to use a varactor diode of relatively small dimensions orsmall over-all geometry, in order to achieve efiicient high-speedswitching. Such a diode may be of any commercially available reactivetype such as, for example, type MA 4352, Style D, manufactured byMicrowave Associates, Inc. (Semiconductor Division), of Burlington,Mass. Accordingly, the use of a waveguide of reduced height ispreferred, in order to maximize the switching effect of the diode uponthe impedance of the waveguide section, as is explained more fullyhereinafter.

The cooperation of diode 18 shunted across the narrow dimension ofwaveguide section 17 is designed to provide a parallel-tuned tank ofinfinite shunt impedance to microwave signals of a preselectedfrequency, including frequencies as high, for example, as 9.3kilomegacycles per second. Such tank is of an extremely high Q becausethe varactor diode is essentially a capacitive or reactive diode (asdistinguished from resistive diodes), the reactive effect of which isvaried by adjustment of a bias potential applied across the electrodeterminals (18a and 18b) thereof. Because of the small overall geometryof varactor 18, the associated inductive parameter is minimized. Hence,the response time of the diode is minimized, whereby high speedswitching of the diode may be achieved. Diodes of the type described maybe switched at switching frequencies at least as high as 100 megacyclesper second, the actual speed in practice being limited mainly by thespeed of the driver circuit.

Because of the small overall geometry (in addition to essentiallyreactive nature) of varactor 18, the resistive (or energy dissipative)parameter thereof is minimized. Further, where a reduced heightwaveguide is employed, dissipative or lossy structure (such as theelectrical terminals at either end of the diode and associatedsupporting structure for supporting the diode) are exterior to, orexcluded from, the waveguide section 17. Because the lossy structure isexcluded from the waveguide section 17, essentially loss-lesstransmission may be effected thru the waveguide, when the bias potentialapplied across terminals 18a and 18b of diode 18 is adjusted to providea tuned shunt tank. Accordingly, when the tank is detuned (relative tothe preselected frequency of interest) by switching or adjusting thebias potential to another value, the detuned or reduced shunt impedanceis essentially reactive in nature, whereby microwave energy reflectionoccurs (rather than dissipation), the energy applied to either end ofthe waveguide being reflected back to such end. The range of voltagesemployed in switching diode 14 are on the order of about 1 to 10 volts.

In FIG. 4, an adjustable tuning slug 44 is shown slidably mountedvertically above diode 18 in the upper mounting cavity 45 exterior towaveguide section 17, and is provided for adjustment of the tuning ofthe tank to a desired tuning frequency, as is well understood in theart. The cavity 46 vertically below diode 18 and external to waveguidesection 17 is a half wavelength section, comprising two mutuallyconcentric quarter wavelength sections 47 and 48 connected by annularaperture 49, whereby a half-wavelength choke impedance is provided, asis well understood in the microwave art. The purpose of such choke is toprevent leakage of microwave energy out of the switch to the synchronousswitching signal source 19 (in FIG. 2) along a switching line (notshown) connected to connector 50.

Upper diode terminal 18a is grounded to the waveguide structure by meansof electrical contact with mechanical mounting post 33. Lower diodeterminal 18b is electrically connected to connector terminal 50 by meansof electrical contact with the mechanical mounting provisions at theupper end of connector terminal 54] which connector terminal iselectrically insulated from the wave guide structure. Hence, switchingsignals may be applied across diode 18 by connecting a source of suchsignals to the waveguide section and connector terminal 59.

Because of the reduced height waveguide employed, quarter wavetransition sections or microwave step transformers 17a and 17b areemployed at either end of waveguide section 17 in order to achieveimpedance matching with the microwave sources connected thereto, as iswell understood in the microwave art.

Hence, it is to be appreciated that the structure illustrated in FIGS. 3and 4 cooperate to provide alternately transmissive and reflectivestates to microwave energy of a preselected frequency, in response tohigh-speed switching signals of switching frequencies as high asmegacycles per second.

Therefore, it is to be understood that, .in the exemplary application inFIG. 2, the periodic operation of switch 14 in response to periodicswitching signals, alternately reflects and transmits energy appliedthereto, whereby alternately 1) the output energy from the second portof circulator 10 is reflected to the third or output port thereof, whilethe output energy from the second port of circulator 11 is reflected tothe shorting impedance 16 across the third port thereof; and (2) theoutput energy of the second port of circulator 10 is transmitted thruthe second "andthird ports of circulator 1 1 to shorting impedance 16,while the output energy from the second port of circulator 11 istransmitted thru the second and third ports of circulator .10 to outputline 15.

An alternate embodiment of the device of FIG. 2, and which employs threecirculators, is shown in FIG. 5.

Referring to FIG. 5, there is illustrated a block diagram of a pulsedradar system employing an alternate embodiment of the invention. Thereis provided a source 38 of pulsed microwave energy and a transmittingand receiving radar antenna 35 having at least two apertures 36 and 37.Antenna 35 is operatively coupled for radiating or transmittingmicrowave energy generated by source 38, Antenna 35 will also provide atapertures 36 and 37 microwave echoes (of the transmitted microwaveenergy) or other microwave signals received thereby, as 'is wellunderstood in the art. Microwave energy source 38 may be of any typeusual in the art for providing microwave energy. Such source might beadapted, for example, for providing pulsed micro-wave energy having apulsewidth andfurther having a pulsing interval substantially in excessof the duration of the pulsewidth.

The construction and arrangement of multi-aperture antenna 35 andmicrowave generator 38 are well-known in the art, as is indicated byFIG. 3 of U.S. Patent 2,933,- '980, issued on April 26, 1960 to J. R.Moore et al. for an Integrated Aircraft and Fire Control Autopilot. Ac-

cordingly, elements 35 and 38 are shown in block form only.

There is also provided a first, second and third ferrite four-portcirculator 30, 31 and 32. Such four-port circulators may be ofanycommercially available type, such as for example, the ferrite typeModel 900R manufactured by Microwave Development Laboratories, Inc., ofNatick, Massachusetts. A respective first port of first and secondcirculators 30 .and 3-1 is connected to a first and second source 36 and37, respectively, of received microwave energy. Such sources might becomprised for example, of the several apertures of monopulse receivingantenna 35. Magic tee 39 (or like microwave. energy divider means)interconnects the output of microwave energy source 38 with the lastport of each of circulators 30 and 31.

A second port .of each of circulators 30 and 31 is operatively connectedto a first and second port respectively of third circulator 32.Interposed between the second and third circulators 31 and 32 is amicrowave switch 14 of the type described in connection with FIGS. 2, 3and 4, and adapted to be operated (e.g., switched) by source 19 at afrequency representing a periodicity of no more than one-half thepulsewidth of the pulsed energy from source 38.

If desired, microwave signal-limiters 4 2 and 43 may be interposedbetween microwave energy source 38 and switch 14, in order to protectthe switching varactor from damage or malfunction clue to possibleenergy leakage of high level microwave energy from the circulatorsduring the duty cycle of source 38. Such limiter devices are well knownin the art and may be comprised, for example, of a self-biasing varactordiode shunted across a waveguide section, whereby high energy levels ofapplied microwave energy result in an induced voltage or bias across thevaractor which causes energy reflection, thereby protecting circuitelements between which such limiters are interposed. Such reflectedenergy is shunted to ground by means of the shorting impedances shown atthe conductive adjacent par-ts of the four-port configuration ofcirculators 30 and 31 of FIG. 5.

By means of the above described arrangement, efficient and reliablesolid state multi-function switching means is provided for the switchingof microwave signals, including the switching of transmitted andreceived signals and the alternate sampling of several sources ofreceived microwave signals.

In normal operation of the device of FIG. 5, pulsed microwave energygenerated by source 38 travels via en ergy divider 39 to the last portsof first and second circulators 30 and 31, thru those circulators to theadjacent conductive or first ports thereof in substantially unattenuatedform, and thence from the first ports of circulators 30 and 31 toapertures 36 and 37 respectively of antenna 35, where the energy isradiated or transmitted, as is well understood in the art. The echoes ofthe transmitted energy, reflected by radar targets, are received byapertures 36 and 37 of antenna 35, and transmitted to a first port ofcirculators 3t and 31 respectively. The received energy applied to thefirst port of each of circulators 3i) and 32 appears as an output of thecorresponding adjacent conductive or second port of circulators 30 'and31.

Now, varactor switch 14 is periodically switched from a conductive stateto a reflective state and back again to a conductive state, in a likemanner as was explained in connection with the description of switch .14in FIG. 2.

When switch 14 is in the conductive state, received microwave energy(from antenna aperture 36) is applied to the first port of thirdcirculator 32 from the second port of first circulator 30, and thencefrom circulator 32 thru switch 14 and circulator 31 to shortingimpedance 16. Concurrently, received microwave energy (from aperture 37of antenna 35) occurring as an output at the second port of secondcirculator 31, is transmitted thru microwave switch 14 to the secondport of third circulator 32, thence thru the adjacent conductive orthird port of third circulator 32 to output line 15. In other words, inthe conductive state of switch 14, microwave signals received at antennaaperture 36 are shorted thru shorting impedance 16, while microwavesignals re ceived by antenna aperture 37 are transmitted to output line15.

When switch 14 is in the reflective state, received microwave energy(from aperture 36), which is applied to the first port of thirdcirculator 3-2 from the second port of first circulator 30, is againtransmitted thru the second port of third circulator 32 to switch 14.However, because of the reflective state of switch 14, this energy isreflected back to the second port of circulator 32 and is transmittedthru the adjacent conductive or third port to output line 15.Concurrently, received microwave energy (from aperture 37), occurring asan output at the second port of second circulator 31, is transmitted toswitch 14, is reflected therefrom back to the second port of circulator31, and thence thru the third or adjacent conductive port to shortingimpedance 16. In other words, in the reflective state of switch 14,microwave signals received at antenna aperture 36 are transmitted tooutput line 15, while microwave signals received by antenna aperture 13are shorted thru shorting impedance 16.

An alternative embodiment of the invention, which provides theperformance features of FIG. 5 and employs no more than two circulators,is shown in FIG. 6.

Referring to FIG. 6, there is illustrated an alternative embodiment ofthe invention. There is provided an antenna 35, microwave energy source38, and microwave switch 14, similar to like referenced elements of FIG.5. There is also provided a first and second four-port circulator 40 and41 constructed and arranged similarly as the four-port circulators ofFIG. 5. A first port of circulators 40 and 41 is operatively connectedto apertures 36 and 37 respectively of antenna 35; the second ports ofcirculators 40 and 41 being interconnected by microwave switch 14. Thethird port of second circulator 41 is shorted by means of a shortingimpedance 16, while the third port of first circulator 40 serves as anoutput port in cooperation with output line 15.

The last or fourth ports of circulators 40 and 41 are commonly connectedto microwave source 38 by means of energy divider 39, in a like manneras was explained in connection with the divider of FIG. 5.

The normal operation of the device of FIG. 6 may be deduced from theoperational modes explained in connection with FIGS. 2 and 5. The energyfrom source 38, as fed to the fourth or last ports of circulator 40 and41, appears as an output at the conductive adjacent or first ports ofcirculators 40 and 41, whence it is conducted to antenna 35, in asimilar manner as was explained in connection with the cooperation ofthe antenna 35 and source 38 of FIG. 4.

A conductive state of switch 14 in FIG. 6 causes received energy fromaperture 36 to be shorted by impedance 16, and causes received energyfrom aperture 37 to appear at output line 15; while a reflective stateof switch 14 causes received energy from aperture 37 to be shorted byimpedance 16 and causes received energy from aperture 36 to appear atoutput line 15. Hence, a sampling of received energy from apertures 36and 37 is provided by the alternately reflective and transmissive statesof switch 14 (in cooperation with switching signal source 19), in amanner similar to that explained in connection with the device of FIG.2.

While the illustrated embodiments of the invention have describedstructure useful for achieving duplexing and time-sharing of signals,particularly microwave signals, it is to be understood that the conceptof the invention is equally useful to multiplexing or switching ofsignals including microwave signals in a computer or other dataprocessor employing a plurality of such signals.

Thus, the device of the present invention provides a novel and eflicientcombination for effecting switching of electrical signals.

Although the invention has been described and illus trated in detail itis to be clearly understood that the same 18 by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this lnvention being limited only by the terms of the appendedclaims.

I claim:

1. The combination comprising A first and second microwave circulator,each having at least three ports,

A respective first port of said circulators being adapted to beconnected to a first and second source respectively of microwave energy,

A microwave switch interconnecting the second ports of said circulators,and adapted to be operatively connected to a source of switchingsignals,

A third port of one of said circulators being shorted through a loadimpedance, and a third port of the other of said circulators providing asampled output.

2. The combination of claim 1 in which said microwave switch comprises Awaveguide section,

A varactor diode shunted across said waveguide section and adapted tocooperate therewith alternatively as a tuned waveguide circuit and as areflector of microwave energy applied at either end of said waveguidesection, in response to signals applied across said diode.

3. Microwave switching means comprising A first and second microwavecirculator having at least three ports,

A first port of said first and second circulators being connected to amutually exclusive one of two sources of microwave energy,

A third port of said second circulator being shorted through a shortingimpedance,

Microwave means interconnecting the respective second ports of saidfirst circulator and said second circulator for alternately reflectingmicrowave energy received from one of said sources through said shortingimpedance and transmitting microwave energy received from the other ofsaid sources through said shorting impedance, whereby the receivedenergy of alternate ones of said mutually exclusive sources of microwaveenergy is transmitted to a third port of said first circulator as anoutput thereof.

4. The device of claim 3 in which said microwave means comprises Asource of a two-state control voltage, and

A voltage-controlled microwave impedance interconnecting a second portof said first and second circulators for alternately providing microwavecommunication therebetween and reflection of microwave signals inresponse to a respective state of said two-state control voltage.

5. The microwave combination comprising A first ferrite circulatorhaving at least three ports;

A second and third ferrite circulator, each having at least four ports;

A respective first port of said second and third circulator connected toa first and second source, respectively, of received microwave energy;

A respective second port of said second and third circulator beingconnected to a first and second port, respectively, of said firstcirculator, and a third port of said third circulator being shunted by adissipative shunt impedance;

A microwave switch interposed between said first and third circulator,

A third source of pulsed microwave energy having a preselectedpulsewidth and a pulsing interval substantially in excess of theduration of said pulsewidth,

Energy divider means operatively connected to divide said pulsedmicrowave energy between a third and fourth port of said second andthird circulator, respectively,

Said microwave switch being adapted to be operated at a frequencyrepresenting a periodicity of no more than one-half the pulsewidth ofsaid pulsed energy.

6. The device of claim 5 in which there is further provided signallimiting means interposed between said first and second circulators andbetween said third circulator and said microwave switch.

7. The device of claim 6 in which said signal limiting means iscomprised of a varactor diode shunted across a waveguide section.

8. Microwave-switching means comprising A first and second microwavecirculator having at least three ports,

A third circulator having at least four ports,

A first port of said first and third circulators being connected to amutually exclusive source of microwave energy,

A third port of said third circulator being shorted through a shortingimpedance,

Microwave means including a first and second port of said secondcirculator and interconnecting the second ports of said first and thirdcirculators for alternately reflecting said microwave energy received bysaid third circulator through said shorting impedance and transmittingsaid microwave energy received by said first circulator through saidshorting impedance whereby the received energy of alternate ones of saidfirst and third circulators is transmitted to an output port of saidsecond circulator, the last ports of said first and third circulatorsbeing adapted to be connected to a third source of microwave energy tobe transmitted.

9. The device of claim 8 in which said microwave means further includesA reduced height waveguide section interconnecting the second port ofsaid second and third circulators,

A second port of said first circulator and a first port of said secondcirculator being interconnected for microwave communicationtherebetween,

A varactor diode shunted across the narrow dimension of said reducedheight waveguide and responsively connected to a source of two statesignal for making said reduced height Waveguide section alternatelyconductive and reflective of microwave signals.

10. Microwave switching means comprising An antenna having at least twoapertures for transmitting and receiving microwave energy,

A source of microwave energy to be transmitted,

Unidirectional microwave means for severally coupling said source ofmicrowave energy to said two apertures, and

Sampling means including said undirectional means for sampling receivedechoes of said microwave energy received by alternate ones of saidapertures,

Said unidirectional microwave means comprising a first and secondferrite microwave circulator having at least three and four portsrespectively, a first port of each of which is connected to a mutuallyexclusive one of said apertures, a last port of each of which iscommonly responsively connected to said source of microwave energy;

Said sampling means further including microwave switch means havingalternatively conductive and reflective states and interconnecting arespective second port of said circulators, and a dissipative shuntimpedance shunting a third port of said second circulator.

References Cited by the Examiner UNITED STATES PATENTS 2,627,020 1/53Parnell et a1 34316 2,988,739 6/61 Hoefer et al 34316.1 3,027,453 3/62Carter et a1. 325-24 3,032,723 5/62 Ring 3337 3,067,394 12/62 Zimmermanet al 307-88.5 3,096,474 7/63 Marie 333-7 3,098,968 7/63 Weinschel et al34317.7 X 3,099,794 7/63 Essam et al 32524 3,108,236 10/63 Medina 33373,113,269 12/ 63 Essam 325-24 FOREIGN PATENTS 638,166 3/62 Canada.

30 CHESTER L. JUSTUS, Primary Examiner.

3. MICROWAVE SWITCHING MEANS COMPRISING A FIRST AND SECOND MICROWAVECIRCULATOR HAVING AT LEAST THREE PORTS, A FIRST PORT OF SAID FIRST ANDSECOND CIRCULATORS BEING CONNECTED TO A MUTUALLY EXCLUSIVE ONE OF TWOSOURCES OF MICROWAVE ENERGY, A THIRD PORT OF SAID SECOND CIRCULATORBEING SHORTED THROUGH A SHORTING IMPEDENCE, MICROWAVE MEANSINTERCONNECTING THE RESPECTIVE SECOND PORTS OF SAID FIRST CIRCULATOR ANDSAID SECOND CIRCULATOR FOR ALTERNATELY REFLECTING MICROWAVE ENERGYRECEIVED FROM ONE OF SAID SOURCES THROUGH SAID SHORTING IMPEDANCE ANDTRANSMITTING MICROWAVE ENERGY RECEIVED FROM THE OTHER OF SAID SOURCESTHROUGH SAID SHORTING IMPEDANCE, WHEREBY THE RECEIVED ENERGY OFALTERNATE ONES OF SAID MUTUALLY EXCLUSIVE SOURCES OF MICROWAVE ENERGY ISTRANSMITTED TO A THIRD PORT OF SAID FIRST CIRCULATOR AS AN OUTPUTTHEREOF.